Modifying the schema definition of an attribute which exists in your
directory is definitely a bad idea. I didn't know that you can crash
slapd by merely adding an EQUALITY rule, but it doesn't surprise me
either. The safe way is to slapcat the database before the schema
change and slapadd it back afterwards.

If an EQUALITY rule is added to an attribute that is already present in
the database, slapd assumes it knows how to normalize its values and, in
some places it may expect that the normalized values be already present
in the database. Maybe this crash needs to be investigated as soon as
the possibility to modify the schema run-time is released.